The present invention relates to an improved process for the preparation of a catalyst useful for liquid-liquid sweetening of LPG and light petroleum distillates.
More particularly the invention relates to the preparation of sulphonamides of various metal phthalocyanines suitable as catalysts and their use for liquid-liquid sweetening of pentanes, LSRN, cracked naphtha and regeneration of alkali in the extraction of mercaptans from LPG, pentanes, LSRN and light thermally cracked naphtha.
It is well known that the presence of mercaptans in the petroleum products like LPG, naphtha, gasoline, kerosene, ATF etc is highly undesirable because of their foul odour and highly corrosive nature. They are also poisonous to the catalysts and adversely affect the performance of tetraethyl lead as octane booster. Although there are several processes known for the removal of mercaptans from petroleum products, the most common practice is to oxidize the mercaptans present to less deleterious disulphides with air in the presence of a catalyst. Generally, the lower mercaptans present in LPG, pentanes, LSRN and light thermally cracked naphtha are first extracted in alkali solution and then oxidized to disulfides with air in the presence of a catalyst. The disulphides, being insoluble in alkali solution, separate out from the top and the alkali is regenerated. In the liquid-liquid sweetening the lower mercaptans present in petroleum products like pentanes, LSRN, cracked naphtha etc are converted to disulphides by direct oxidation with air in the presence of alkali solution and catalyst. The higher molecular weight mercaptans present in petroleum products like heavy naphtha, FCC gasoline, ATF and kerosene are oxidized to disulphides with air in a fixed bed reactor containing catalyst impregnated on a suitable support like activated carbon (Catal. Rev.-Sci. Eng. 35(4), 571-609 (1993).
It is also well known that the phthalocyanines of the metals like cobalt, iron, manganese, molybdenum and vanadium catalyze the oxidation of mercaptans to disulphides in alkaline medium. Among these cobalt and vanadium phthalocyanines are preferred. As the metal phthalocyanines (MPC""s) are not soluble in aqueous medium, for improved catalytic activity their derivatives like sulphonated and carboxylated metal phthalocyanines are used as catalysts for sweetening of petroleum fractions. For example use of cobalt phthalocyanine monosulphonate as the catalyst in the fixed bed sweetening of various petroleum products (U.S. Pat. Nos. 3,371,031; 4,009,120; 4,207,173; 4,028,269; 4,087,378; 4,141,819, 4,121,998; 4,124,494; 4,124,531) and cobalt phthalocyanine disulphonate (U.S. Pat. No. 4,250,022) tetra sulphonate (U.S. Pat. No. 2,622,763) and the mixture thereof (U.S. Pat. No. 4,248,694) as catalysts for liquid-liquid sweetening and alkali regeneration in mercaptan extraction of light petroleum distillates have been reported. The use of phenoxy substituted cobalt phthalocyanine as sweetening catalyst (Ger Offen 3,816,952), cobalt and vanadium chelates of 2,9,16,23-tetrakis (3,4-dicarboxybenzoyl)phthalocyanine as effective catalyst for both homogeneous and fixed bed mercaptan oxidation (Ger Offen 2,757,476; Fr. Demande 2,375,201) and cobalt, vanadium chelates of tetrapyridinoporphyrazine as active catalysts for sweetening of sour petroleum distillates (Ger offen 2,441,648) have also been reported.
It is well known that the catalysts used for the liquid-liquid sweetening of petroleum fractions like pentanes, LSRN, etc. and regeneration of alkali in the mercaptan extraction from LPG, pentanes etc are di-, tri-and tetra sulphonates of metal phthalocyanines particularly those of cobalt and vanadium phthalocyanines; cobalt phthalocyanine sulphonates being specially preferred. The cobalt phthalocyanine sulphonates differ in activity and in their solubility characteristics depending upon the number of sulphonate functionalities leading to problems in their use as catalysts.
Cobalt phthalocyanine disulphonate, a commonly used catalyst in liquid-liquid sweetening and alkali regeneration, is extremely dusty in the dry fine powder form and causes a handling problem. To overcome this problem cobalt phthalocyanine disulphonate is admixed with water and commonly used as a slurry. However, with insufficient mixing the cobalt phthalocyanine disulphonate precipitates out from the slurry. Moreover, even if the slurry is mixed sufficiently, it retains the cobalt phthalocyanine disulphonate in suspension for a particular length of time only, beyond which the slurry becomes extremely viscous and may form gel, making it very difficult to remove the material from packaging. Cobalt phthalocyanine tetrasulphonate, on the other hand, is highly soluble in water and its use can eliminate precipitation and gel forming problems associated with the use of cobalt phthalocyanine disulphonate. However, it is reported that cobalt phthalocyanine tetrasulphonate has lower catalytic activity than cobalt phthalocyanine disulphonate (U.S. Pat. No. 4,885,268). Further, preparation of the metal phthalocyanine disulphonates by reacting metal phthalocynines with oleum has handling and working-up problems.
During our investigations on the development of new sweetening catalysts, we observed metal phthalocyanine sulphonamides to be active catalysts for liquid liquid sweetening of light petroleum products (Indian Patent No 1,53,190, Indian 5Patent No. 1,52,541 and Ind. J. Tech. 25, 397-400 (1987)). In these patents and literature a procedure for making cobalt phthalocyanine sulphonamides has been reported. This method involves treatment of cobalt phthalocyanine with chlorosulphonic acid followed by amidation with ammonia gas. However, the catalyst yield and activity was found to be low. Hence the present invention provides an improved process for the preparation of metal phthalocyanine sulphonamides in considerably higher yields and with very high catalytic activities for both liquid-liquid sweetening and alkali regeneration.
The objective of the present invention is to provide an improved process for the 15preparation of metal phthalocyanine sulphonamide suitable a catalyst for liquid-liquid sweetening of pentanes, LSRN, cracked naphtha etc. and regeneration of alkali in the mercaptan extraction from LPG, pentanes, LSRN, light thermally cracked naphtha and the like, which obviates the drawbacks as detailed above.
Accordingly the present invention provides an improved process for the preparation of catalyst metal phthalocyanine sulphonamide of the formula 
Mpc(SO2NHR)x 
wherein MPc represents 
xe2x80x83M is Co, Ni, Fe, Mn, Cr or V;
X is 1, 2, 3 or 4 and
R is hydrogen, alkyl,or cycloalkyl,
useful for LPG and light petroleum distillates which comprises;
reacting a metal phthalocyanine with chlorosulphonic acid at a temperature in the range of 90-150xc2x0 C. for a period ranging between 1 hr-5 hrs, cooling the mixture to a temperature ranging between 40-80xc2x0 C., adding 1-7 parts of a chloride reagent to the said mixture, heating the above said mixture to a temperature ranging between 60-80xc2x0 C for a period ranging between 0.5 hr to 3 hrs to obtain the metal phthalocyanine sulphonyl chloride, isolating the above said compound by adding the reaction mixturein an ice cold water, reacting the above isolated metal phthalocyanine sulphonyl chloride with an amine of general formula H2NR where R is selected from hydrogen, aryl, alkyl and cycloalkyl in an aqueous or non aqueous medium or a mixture thereof at a temperature in the range xe2x88x924 to 15xc2x0 C. and at a pH ranging between 7-9 in the presence of an acid binding agent to obtain the desired catalyst.
In an another embodiment of the present invention the metal phthalocyanine used is selected from the group consisting of cobalt, manganese, iron, nickel, chromium and vanadium phthalocyanine, most preferably cobalt phthalocyanine.
In yet another embodiment of the present invention the chloride reagent used is selected from thionyl chloride, phosphorus trichloride and phosphorus pentachloride.
In yet another embodiment of the present invention the non-aqueous medium used is to selected from the group consisting of chlorobenzene, nitrobenzene, alcohols and N, N--dimethylformamide.
In yet another embodiment of the present invention the acid binding agent used is selected from the group consisting of sodium bicarbonate, sodium carbonate, sodium hydroxide and tertiary organic bases selected from pyridine, triethyl amine and piperidine. In yet another embodiment of the present invention the catalyst prepared is metal phthalocyanine sulphonamide selected from the group consisting of cobalt, manganese, nickel, iron, vanadium phthalocyanine sulphomamide and their N-substituted sulphonamide derivatives, most preferably selected from cobalt phthalocyanine tetra-sulphonamide and cobalt phthalocyanine tetra-N-(4-hydroxy phenyl)sulphonamide.
In still another embodiment of the present invention the metal phthalocyanine sulphonamide catalyst is useful for both liquid-liquid sweetening and alkali regeneration in the mercaptan extraction from petroleum fraction such as LPG, pentanes, light straight run naphtha and cracked naphtha.
In the present invention the sulphonamides of the metal phthalocyanines suitable as sweetening catalysts are prepared by first converting the suitable metal phthalocyanine to the corresponding metal phthalocyanine sulphonyl chloride (mono-, di-, tri-, tetrasulphonyl metal phthalocyanine or a mixture thereof) followed by reacting the metal phthalocyanine sulphonyl chlorides with different amines including ammonia to yield the metal phthalocyanine sulphonamides.
According to the present invention one part of suitable metal phthalocyanine is slowly added to 5-20 parts of chlorosulphonic acid at room temperature. The temperature of the reaction mixture is slowly increased in stages to 90-150xc2x0 C. and maintained at this temperature for 1-5 hrs. The reaction mixture is then preferably cooled to 40-80xc2x0 C. and 1-7 parts of thionyl chloride or phosphorus pentachloride or phosphorus trichlonde or similar such reagent is slowly added. After this addition, in case of thionyl chloride the reaction mixture is heated to 60-80xc2x0 C. and maintained at 20 this temperature for 0.5-3 hrs. In case of other reagents the reaction mixture is heated to a suitable temperature for a suitable period. The metal phthalocyanine sulphonyl chloride thus formed is isolated by any suitable technique like hydrolysing the reaction mixture with ice cold water. This yields 1.6-1.69 parts of metal phthalocyanine sulphonylchloride with metal phthalocyanine tetrasulphonyl chloride as major component and trisulphonyt-, disulphonyl chlorides as the minor components.
Similarly metal phthalocyanine mono-, di-, tri-, tetrasulphonic acid or mixture thereof is converted into the corresponding metal phthalocyanine sulphonyl chlorides in almost quantitative yields, by adding one part of the former to 3-8 parts of chlorosulphonic acid or similar such solvent at room temperature preferably under cooling conditions, heating the reaction mixture to 60-80xc2x0 C. and then adding 1-5 parts of reagents like thionyl chloride or phosphorus pentachloride or phosphorus trichloride or the like. The reaction is completed by heating for 0.5 to 5 hrs at a suitable temperature.
The present invention provides an improved methodology for the conversion of metal phthalocyanine sulphonyl chlorides, thus obtained, in to the corresponding metal phthalocyanine sulphonamides suitable as catalysts for the liquid-liquid sweetening and alkali regeneration in the mercaptan extraction. The suitable metal phthalocyanine sulphonamides havexe2x80x94SO2NHR group where R may be hydrogen, alkyl, cycloalkyl, aromatic or any other group like substituted aromatic or long chain alkyl with further substitution with different functional groups. The metal phthalocyanine sulphonamides with xe2x80x94SO2NR1R2xe2x80x94, without any hydrogen attached to nitrogen, in general are not found suitable as sweetening catalysts due to their limited solubility in alkali solution. The metal phthalocyanine sulphonamides are prepared by reacting metal phthalocyanine sulphonyl chlorides with suitable amines of general formula H2NR where R may be hydrogen, alkyl, cycloalkyl, aromatic or any other group either in the form of free base or in the form of their water soluble hydrochloride or any other acid salt. The reaction of metal phthalocyanine sulphonyl chlorides with amines can be carried out in aqueous or non-aqueous medium such as chlorobenzene, nitrobenzene, alcohols, or N, N-dimethylformamide in the presence of acid-binding agents. The suitable acid-binding agents are sodium bicarbonate, sodium carbonate, sodium hydroxide, tertiary organic bases such as pyridine or triethylamine or an excess of the amines used for making sulphonamide. The reaction is carried out at pH values in a weakly acidic to alkaline ranges.
The improved method of this invention for the preparation of metal phthalocyanine sulphonamides with SO2NH2 groups consists of dispersing the wet cake of metal phthalocyanine sulphonyl chloride in water, alcohol or their mixture or similar such medium and passing ammonia gas either after bringing the pH of the system to about 7.00 or without pH adjustment at 0-20xc2x0 C. temperature till the reaction mixture is fairly alkaline. To this reaction mixture catalytic amount of any organic base like pyridine, piperidine, triethylamine, and alkali solution, either both or one of them is added. The reaction mixture is then stirred at room temperature for 10-120 minutes and at 30-90xc2x0 C. for 10-60 minutes. The metal phthalocyanine sulphonamide is isolated by acidification of reaction mixture.
Various metal phthalocyanine sulphonamides specially those of cobalt, manganese, iron and vanadium prepared according to this invention were found to be active catalysts for liquid-liquid sweetening of pentanes, LSRN, cracked naphtha and the like, and regeneration of alkali in the mercaptan extraction from LPG, pentanes, LSRN, and light thermally cracked naphtha. The cobalt phthalocyanine sulphonamides prepared according to the improved process of this invention were found to be crystalline compounds unlike cobalt phthalocyanine disulphonate, which is extremely dusty, and can be handled without problems. These catalysts can be used directly by dissolving in alkali and no prior admixing with water is required. Unlike cobalt phthalocyanine tetrasulphonate, cobalt phthalocyanine sulphonamide prepared according to the improved method of this invention were found to be very active catalysts for liquid-liquid sweetening and alkali regeneration. As the metal phthalocyanine sulphonamide prepared according to this invention is insoluble in acidic media, they could be easily isolated.
The present invention provides an improved method for the preparation of suitable metal phthalocyanine sulphonyl chlorides which involves first treating the metal phthalocyanines with chlorsulphonic acid followed by addition of thionyl chloride to the reaction mixture. In place of thionyl chloride, phosphorus pentachoride or phosphorus trichloride or any other such reagent can also be used. The novelty of the present invention lies in the addition of thionyl chloride or such reagent which was found to be necessary to ensure complete conversion of all the sulphonic acid groups to sulphonyl chloride followed by ammination in a single step to get maximum yield of metal phthalocyanine sulphonamide.